1. Field of the Application
The present application relates generally to a new method for drilling using microwave energy.
2. Description of the Related Art
The current state of the art in drilling rock utilizes rotating drilling bits to fracture rock into small pieces, which are then removed from a hole by a circulating fluid. This process takes time to drill any distance, and the harder the rock is the longer it takes to drill that distance. In order to speed up drilling in harder rock, harder drill bits are used. Very hard rock is drilled using bits that are not only made of hard metals, but that also have diamond fragments glued to the cutting faces of the drill bit (e.g., the rollers of the drill bit). Such drill bits nevertheless wear out regularly when used to drill very hard rock, and have to be replaced, a process which takes additional time. The drill string has to be removed from the borehole by disassembling it, so that the worn-out bit can be replaced, and then the new bit is lowered into the borehole by reassembling the drill string. The problems and delays are made worse if the rock is hot, because the heat causes the diamond fragments to become detached from the bit, so that the bit becomes worn out even sooner. The heat can also cause other malfunctions in the drilling of the borehole, and can complicate the collection of data regarding the progress of the drilling, making it more difficult to control the drilling.
Some recent studies have analyzed the use of flame-jets or lasers to heat the surface of the rock to be removed, causing the spalling of the rock surface. Such methods may not work effectively, depending on the characteristics of the rock that is being drilled. For example, some kinds of rock are not susceptible to spalling.